Final answer:
Hereditary angioedema is most commonly caused by a deficiency in the C1 inhibitor (C1-INH), particularly in cases of Type I hereditary angioedema, which represents 80%-85% of all cases.
Step-by-step explanation:
The protein deficiency associated with hereditary angioedema is C1 inhibitor (C1-INH) deficiency. Hereditary angioedema is a genetic disorder that can lead to occasional episodes of swelling in various parts of the body, including the respiratory and gastrointestinal tracts. This disorder can be caused by a deficiency in C1 esterase inhibitors (C1-INH), which are proteins that normally help to suppress activation of the complement system. When these proteins are deficient or nonfunctional, this can result in the overstimulation of the system and the production of inflammatory substances that cause tissue swelling and fluid buildup.
Type I hereditary angioedema accounts for 80%-85% of all cases and is specifically characterized by a deficiency in C1-INH. There is currently no cure for hereditary angioedema, but treatment with purified and concentrated C1-INH derived from blood donors can be effective in preventing complications.